1. Field Of The Invention
The present invention relates in general to robot machines and in particular to an improved wrist mechanism for a robot arm.
Robot machines are becoming increasingly common in many industries. Such robot machines typically consist of a support unit, a base mounted on the support unit and rotatable about a vertical axis, and a lower arm mounted on the base and pivotable about a horizontal axis. An upper arm is mounted on the upper end of the lower arm and pivotable about a horizontal axis, and a tool supporting unit universally connected to the upper end of the upper arm through a wrist mechanism. In the past, these wrist mechanisms have been complicated and expensive, while providing only marginally satisfactory performance. Furthermore, many of such wrist mechanisms do not provide any internal passageway for carrying actuating lines to the supported tool. As a result, loose pneumatic, hydraulic, or electrical lines are exposed and may tangle or break because of movement of the robot arm. The prior art wrist mechanisms which do provide an internal passageway for the actuating lines often subject them to extreme angles of bending during movement of the robot arm, thereby promoting fatigue and subsequent failure of the lines.
2. Description Of The Prior Art
U.S. Pat. No. 4,402,234 to Malarz et al. discloses a wrist mechanism having three independent rotational axes with a point of mutual intersection. A stationary housing determines one of the axes, while a second axis is defined by a tool support member. The third axis is determined by an intermediate housing between the stationary housing and the tool support member. The three axes intersect at a single point. A plurality of gear trains provide for independent rotation of the components about the three axes so as to permit selective positioning of the tool support member within a substantially hemispherical envelope. The gear trains are arranged so that an unobstructed enclosed passage is maintained between the stationary base and the tool support member for accommodating actuating lines for a tool mounted on the support member. However, the actuating lines may be subjected to unnecessary stresses since they are both twisted and bent about the point at which the three axes intersect.
British patent application No. 2,147,877A to Dahlquist et al. discloses a wrist for an industrial robot having a large orientation capacity and an unobstructed passage for accommodating tool actuating lines. First, second, third, and fourth turnable wrist parts are arranged in series with each other. The first wrist part is rotatable about a first axis. The second wrist part is journalled in the first part and is rotatable about a second axis which intersects the first axis. The third wrist part is journalled in the second part and is rotatable about a third axis which intersects the second axis. Tool attachment means constituting the fourth wrist part are rotatably journalled in the third wrist part about a fourth axis which intersects the third axis.
U.S. Pat. No. 4,068,536 to Stackhouse discloses a manipulator which orients an end effector mounted to one end of a plurality of serially connected drive shafts. The manipulator has two sets of concentric shafts, with individual shafts within each set independently rotatable about an axis common to the set. The common axes of the two sets are obliquely oriented with respect to each other. A third shaft, rotatable about a third axis, is angularly oriented and connected to the most remote set of shafts.
Other similar devices are disclosed in U.S. Pat. Nos. 3,375,727 to Nasvytis et al., 4,353,677 to Susnjara et al., 4,365,928 to Bailey et al., and 4,499,784 to Shum.